In general, Wi-Fi systems are considered energy-consuming, so have yet to be widely applied to sensor network and IoT. Fortunately, passive Wi-Fi devices were developed in 2016 to improve the power consumption of the conventional Wi-Fi systems.
FIG. 1 shows a currently available passive Wi-Fi device 1, which includes a frequency synthesizer 11, a baseband processor 12, a backscatter modulator 13 and an antenna 14.
The frequency synthesizer 11 and the baseband processor 12 are connected to the baseband process or 12 and the backscatter modulator 13.
The baseband processor 12 is connected to the backscatter modulator 13.
The backscatter modulator 13 can transmit data to the antenna 14; when the antenna 14 receives the signals from another electronic device, the antenna 14 can be powered by absorbing the energy of the received signals, and simultaneously transmit the data to the electronic device. Thus, radio waves can simultaneously carry data and electricity via the backscatter communication, so the passive Wi-Fi device 1 can mutually communicate with other electronic devices without power supply.
The passive Wi-Fi device 1 can transmit the wireless signal based on 802.11b, and can directly communicate with various mobile devices, such as smart phones tablet computers, etc.; besides, the passive Wi-Fi device 1 can significantly reduce the power consumption, so can effectively import the drawback of conventional Wi-Fi devices.
However, the passive Wi-Fi device 1 cannot concentrate its beam pattern on a specific direction, so cannot effectively receive signals transmitted from another electronic device, or transmit signals to another electronic device; accordingly, the radio coverage of the passive Wi-Fi device 1 can never be effectively increased. Further, data transmitted by the passive Wi-Fi device 1 tend to leak, so the passive Wi-Fi device 1 cannot insure the information security of users.
Therefore, how to provide a passive Wi-Fi device capable of improving the shortcomings of currently available passive Wi-Fi devices has become an important issue.